Fluorescent and colorimetric dual-readout sensor based on Griess assay for nitrite detection

In this work, we presented a sensitive and selective colorimetric and fluorescent dual-readout sensor based on Griess assay for nitrite (NO₂^-) detection under acidic condition. The sensor system was constituted of acid-resistant carbon quantum dots (CQDs) and 3-aminophenol (3-Aph) with acidic condition regulated using HCl. During the sensing procedure, reaction of 3-Aph and NO₂^- under acidic condition can yield a yellow-colored azoic compound (AZO), which gives the colorimetric readout; meanwhile, the fluorescence of CQDs (fluorescence reporter) quenched due to the strong absorption of AZO, leading to fluorescent readout. Wherein, CQDs were synthesized via hydrothermal method through using polyacrylamide as precursor and characterized by AFM, XRD and XPS. Under the optimized condition, the sensor exhibit broad linear relationships towards NO₂^- in the range of 10 to 100 nM and 2.5 to 100 μM, with practical detection limits of 10 nM and 2.5 μM for the fluorescent and colorimetric readout, respectively. And the sensor displayed excellent capability of selectivity according to interferences study. Furthermore, testing of sprouts, bacon and ham sausage real samples demonstrated good recoveries and reproducibility of the sensor system. All these results suggested the presented colorimetric and fluorescent dual-readout sensor can be a promising candidate for the NO₂^- detection in real applications.